re PR target/50931 ([avr] Support a 24-bit scalar integer mode)

re PR target/50931 ([avr] Support a 24-bit scalar integer mode)

libgcc/
	PR target/50931
	* config/avr/t-avr (LIB1ASMSRC): Add _mulpsi3, _mulsqipsi3.
	* config/avr/lib1funcs.S (__mulpsi3, __mulsqipsi3): New functions.
gcc/
	PR target/50931
	* config/avr/avr.md (mulpsi3): New expander.
	(*umulqihipsi3, *umulhiqipsi3): New insns.
	(*mulsqipsi3.libgcc, *mulpsi3.libgcc): New insns.
	(mulsqipsi3, *mulpsi3): New insn-and-splits.
	(ashlpsi3): Turn to expander.  Move insn code to...
	(*ashlpsi3): ...this new insn.
testsuite/
	PR target/50931
	* gcc.target/avr/torture/int24-mul.c: New testcase.

From-SVN: r182328